The present invention relates to the art of power transfer. Particular application is found in transmitting electrical power to undersea installations and will be described with particular reference thereto. It is to be appreciated, however, that the invention is also applicable to supplying power to other remote or relatively inaccessible locations, particularly under fluid locations, such as submersible pumps, downhole well equipment, or the like.
Heretofore, various techniques have been used for providing power to apparatus in undersea and other remote locations. Inductive-type couplers connected to a power transmission cable with the undersea apparatus to permit safe mating and uncoupling under water, even when powered.
Commonly, low frequency AC voltages were transmitted along the power cable to and across the inductive coupling. One of the problems with coupling lower frequency AC voltages was that a relatively large transformer core was required. Large, laminated steel coupler cores were subject to corrosion, particularly by salt water. Although coatings or nonmagnetic, corrosion-resistant barriers could inhibit corrision, they also increased the gap between the coupler halves, hence, reduced efficiency.
To correct this deficiency, others have transmitted high frequency AC voltages along the power transmission cables to the inductive coupler. Inductive couplers for higher frequencies could use ferrite-type pot cores which were relatively small and relatively immune to salt water corrosion. Moreover, the higher the frequency, the smaller the required core to transmit a given level of power. However, high frequency transmission techniques also had their drawbacks. First, the high frequency signals caused crosstalk from power to communication conductors located in the same cable. Further, high frequency transmissions attenuated more quickly than lower frequency transmissions, rendering the high frequency transmissions unsuitable for long distance power transfers.
The present invention provides an improved power transfer and inductive coupling system which overcomes the above-referenced disadvantages and others of the low and high frequency transmission techniques.